Simultaneous atmospheric CO, N 2 O and H 2 O detection using a single quantum cascade laser sensor based on dual-spectroscopy techniques

A single continuous wave (CW) room-temperature (RT) quantum cascade laser (QCL) sensor based on dual spectroscopic techniques was demonstrated and developed for simultaneous measurement of atmospheric carbon monoxide (CO), nitrous oxide (N2O) and water vapor (H2O). The newly developed detection scheme combines the benefits of absolute concentration measurements using calibration-free direct absorption spectroscopy (DAS) with higher sensitive wavelength modulation spectroscopy (WMS), which offers the possibility of calibration-free trace gases concentration detection with a 3–4 fold improvement in measurement precision and a significant decrease in optimal signal averaging time. By using the DAS calibrated WMS-2f detection scheme, Allan deviation analysis indicates that measurement precision of 1.64 ppb for CO, 1.15 ppb for N2O and 50.4 ppm for H2O was achieved with a 1-s integration time, which can be further improved to 0.21 ppb, 0.18 ppb and 5.65 ppm by averaging up to 75 s.